2000 Chevy Lumina Bangs into gear and shakes while throwing

I have had the valve body with the pressure control solenoid replaced in my tranny as well as the torque converter. My car still shifts hard when its warmed up and makes the ever familiar whining sound. It shifts hard and the longer i drive it the worse it gets. It will literally slam into gear with a loud bang and give the car a good shake. when this all happens my check engine light will come on. The tranny guy says the transmission looks good inside and he cant find anything wrong even after replacing the torque converter and valve body. So all in all what are my other options for why my tranny shifts hard and bangs into gear when its really warm as well as making the car shake while it shifts and throws the check engine light. Fluid is fine, mounts are good, had work done on the tranny and still no good... help!